The present invention relates to an image rotation apparatus which rotates, at high speed, an input image by an angle integer multiple of 90.degree. and stores the rotated image into a page memory, and which can accommodate input image data of different numbers of information bits of one pixel.
In image processing apparatuses, the number of density gradation levels of a pixel is determined by the number of information bits of the pixel. For example, a 2-gradation, black-and-white image is reproduced if the number of information bits is one, and a 4-gradation, light and shade image is reproduced if it is two. Although in general the number of information bits is fixed, it may be the case that the number of information bits is changed in the same image processing apparatus in accordance with the purpose of image processing. For example, the number of information bits is set at one when binary, black-and-white image data is processed, and it is increased when halftone image data is processed. The image processing apparatus is required to be able to perform image rotation for image data of difference numbers of information bits of one pixel.
Japanese Patent Application Unexamined Publication No. Sho. 60-81657 discloses a data control technique in an image rotation apparatus in which memory address control is performed by count increase/decrease control of counters. According to this technique, no problem occurs when the number of information bits of one pixel is fixed. However, when there are different numbers of information bits, a plurality of address control means need to be provided for the respective numbers of information bits, which results in a complicated apparatus. Further, In the case of input image data of different numbers of information bits, the image rotation cannot be performed only by the count increase/decrease control of the counters. In addition, image data supplied from a scanner etc. cannot be rotated and stored into a page memory on a realtime basis.
Japanese Patent Application Unexamined Publication No. Sho. 60-83153 discloses a data storage apparatus which rotates, at high speed, an image of an N.times.N-bit block by cyclic shifting. However, since in this apparatus the image data is required to be input on a block-by-block basis, one-page image data cannot be rotated at high speed such that a plurality of blocks are rotated together.